In "The Economist" Daniel Faraday compares the time on a digital clock from the rocket with the one from the tripod and sees that they are different. The rocket's 30 second journey takes around 30 minutes to arrive on the island. This suggests that Time is moving 60 times slower on the island than in the outside world. This means that 6 days on the island equates to 1 year of 'real' time.
The Island is held in a time bubble by magnetic fields (and perhaps other forces). After the failed moment by Desmond to set the code in, it allowed the Island to come in contact with normal space-time, allowing the plane to crash in the otherwise hidden island. This would also explain the magnetic anomaly encoutered by the two portuguese men working for Penny and the wire which gives the energy source for the time bubble.
The Island being in a time bubble explains why Desmond and eventually Mike, Sawyer and Jin couldn't escape the Island. They were just going forward and appearing in the rear (going in circles). This is explained in Stephen Hawkins "Brief History of Time" (see wormholes)
The amount of time passed between when Regina fired off the rocket and when it arrived on the Island was approximately 31 minutes. This may be a time difference of 31 minutes just at the particular time that Daniel ran the experiment - for example, had he run his beacon/rocket experiment hours later or that evening (after almost 24 hours of being on the island) he may have discovered that it had taken more time than just 31 minutes for the payload to reach the island. It may have taken 41 minutes, 51 minutes or over an hour. It may be that the amount of time lost between those on the 'outside' and those on the island grows bigger and bigger the longer one stays on the island and does not return 'the way that they came in'. This may be why he appeared worried and said it was 'not good' when he compared the digital timers - he suspects that this gap in time between the freighter and his colleagues on the island will only continue to get larger the longer they stay on the island completing their objective(s). Assuming this to be correct, then it may also be the reasoning behind his advice to Lapidus to stay as close as possible to the same course that they flew in on - doing so would limit the extent of 'lost time' between the point that they entered the island.
The radio equipment works as a sort of direct connection between Island-time and outside world, taking all bearings at once - the Kahana radio communication went on a restricted frequency. The signal could have been heard in any other time, but Kahana and island were actually the only two spots in any time who used the specific frequency of the conversation.